Magnesium salts of fatty acids or  Magnesium Stearate is a chemical compound, magnesium salt of stearic acid (octadecanoic acid).

The name defines the structure of the molecule:

• Magnesium is a chemical element with the symbol Mg and the atomic number 12. It is a metal and is essential for many biological processes.
• Stearate refers to the stearic acid part of the molecule. Stearic acid is a fatty acid with eighteen carbon atoms.

The synthesis process takes place in several stages:

• Preparation of stearic acid. Stearic acid is obtained from fats and oils from the saponification or hydrolysis process, followed by isolation.
• Reaction with magnesium salt. Stearic acid is reacted with a magnesium salt, such as magnesium oxide or magnesium carbonate, in an aqueous solution. This reaction forms magnesium stearate and a by-product, such as water or carbon dioxide.
• Precipitation. Magnesium stearate is insoluble in water, so it precipitates out of the solution. The solution is cooled to promote precipitation.
• Filtration and washing. The precipitated magnesium stearate is separated from the solution by filtration. It is washed with water to remove any remaining impurities.
• Drying. Wet magnesium stearate is dried to remove residual water by air drying or using a drying oven.
• Quality control test. The final product is tested to ensure it meets the required specifications. This may involve testing for purity, moisture content and other physical and chemical properties.

 It occurs as a light, white, fine powder, insoluble in water, ethoxyethane, ethanol, ether. Soluble in hot water, hot ethanol. On contact with acids it decomposes into stearic acid and magnesium sal's salts.  Commercially it is not pure, but it is a mixture of Magnesium Stearate and Magnesium Palmitate (C₃₂H₆₂MgO₄) extracted from palm oil.

Magnesium stearate has four types of pseudopolymers: monohydrate, dihydrate, trihydrate, anhydrate.

What it is used for and where it is used

Medical

In the pharmaceutical industry, it is an excipient for solid oral dosage forms. It is used as an essential lubricant in production for tablet dissolution, disintegration and hardness and also:

• Lubricant. Magnesium salts of fatty acids, such as magnesium stearate, are commonly used as lubricants in the manufacture of tablets and capsules. They enhance the flow properties of powders, reducing friction during manufacturing.
• Anti-adherent. Magnesium stearate prevents powders from clumping together in pharmaceutical formulations, ensuring uniform distribution of the active ingredient.
• Binder. In some cases, magnesium stearate can be used as a binder, helping to hold the ingredients in a tablet or capsule together.
• Release Agent. Magnesium stearate can be used as a release agent, preventing the finished product from sticking to manufacturing equipment.

Hydroxypropyl methyl cellulose can prevent drug precipitation caused by magnesium stearate (1). It is used as a lubricant in the nanoprecipitation/ion exchange method (2). This study investigates magnesium stearate used as an essential lubricant in tablet production and its effect on tablet dissolution, disintegration and hardness (3).

Food. 

Labelled as an anti-caking agent with the number E572 in the list of European food additives for chocolate and chocolate derivatives, cocoa, candied fruit etc. where it has an anti-caking function. 

Other uses

In the plastics industry it is used as a lubricant and stabiliser for cellulose acetate, polyvinyl chloride, ABS, resins etc.

Cosmetics 

Anticaking agent. This compound facilitates free flow and prevents aggregation or clumping of substances in a formulation by reducing the tendency of certain particles to stick together

Bulking agent. It regulates the water content, dilutes other solids, can increase the volume of a product for better flow, acts as a buffer against organic acids, helps to keep the pH of the mixture within a certain level.

Colorant. This ingredient has the function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

Moisturizing. This ingredient is responsible for preventing the evaporation of moisture from the skin and improving cellular activity. When exposed to cold or hot air currents, the skin absorbs water from its inner layer to compensate for the evaporated water. If the draught phenomenon persists, the stratum corneum is dry and, if at all, damaged.

The most relevant studies on this chemical compound have been selected with a summary of their contents:

Magnesium Stearate studies

Optimal typical characteristics of Magnesium Stearate as a commercial cosmetic product 

• Molecular Formula   C₃₆H₇₀MgO₄    Mg(C₁₈H₃₅O₂)₂
• Linear Formula   [CH₃(CH₂)₁₆CO₂]₂Mg
• Molecular Weight  591.257 g/mol
• Exact Mass    590.512451
• CAS  557-04-0
• EINECS 209-150-3
• UNII 70097M6I30
• DSSTox Substance ID: DTXSID2027208
• MDL number  MFCD00036391
• PubChem Substance ID 24865972
•  InChI Key    HQKMJHAJHXVSDF-UHFFFAOYSA-L
• SMILES    CCCCCCCCCCCCCCCCCC(=O)[O-].CCCCCCCCCCCCCCCCCC(=O)[O-].[Mg+2]
• IUPAC Name    magnesium;octadecanoate
• ChEBI    CHEBI:9254
• Beilstein  3919702
• NACRES  NA.22

Synonyms:

• Stearic acid magnesium salt
  
• Magnesium octadecanoate
• Magnesium distearate
• magnesium dioctadecanoate
• Octadecanoic acid, magnesium salt
• Dibasic magnesium stearate
• octadecanoic acid magnesium salt

References_________________________________________________________________________

(1) Démuth B, Galata DL, Balogh A, Szabó E, Nagy B, Farkas A, Hirsch E, Pataki H, Vigh T, Mensch J, Verreck G, Nagy ZK, Marosi G. Application of hydroxypropyl methylcellulose as a protective agent against magnesium stearate induced crystallization of amorphous itraconazole. Eur J Pharm Sci. 2018 Aug 30;121:301-308. doi: 10.1016/j.ejps.2018.06.008.

(2) Martínez-Acevedo L, Zambrano-Zaragoza ML, Vidal-Romero G, Mendoza-Elvira S, Quintanar-Guerrero D. Evaluation of the lubricating effect of magnesium stearate and glyceryl behenate solid lipid nanoparticles in a direct compression process. Int J Pharm. 2018 Jul 10;545(1-2):170-175. doi: 10.1016/j.ijpharm.2018.05.002. 

(3) Yamamoto K, Tamura T, Yoshihashi Y, Terada K, Yonemochi E. Effect of Magnesium Stearate Mono- and Dihydrate Dispersibilities on Physical Properties of Tablets. Chem Pharm Bull (Tokyo). 2017;65(11):1028-1034. doi: 10.1248/cpb.c17-00429.